Heart valve disease is a very common problem. Each year, half a million people in the world develop heart valve disease. 200,000 are too sick to be treated, but the rest are treated. At present, the treatment of heart valve disease consists of either heart valve repair or valve replacements. Both methods require open-heart surgery, by the use of total cardiopulmonary by-pass, aortic cross-clamping and arrest of the heart. To certain groups of patients, open-heart surgery is particularly hazardous. However, a less invasive method for repair of heart valves is considered generally advantageous.
Heart valve insufficiency may arise from a dilation of the valve annulus, whereby the leaflets of the heart valve are moved away from each other such that the area of coaptation is minimized or vanished. The area of coaptation is the area where the leaflets of heart valves lean against each other, thereby closing the valve opening sufficiently. Thus, an existing gap or incomplete area of coaptation between the leaflets creates a leak in the valve.
In U.S. Pat. No. 6,210,432, a less invasive method is proposed for treating heart valve insufficiency. Here, a method is described for treatment of mitral insufficiency without the need for cardiopulmonary by-pass and opening of the chest and heart. The method uses a device comprising an elongate body having such dimensions as to be insertable into the coronary sinus, which is a vein that substantially encircles the mitral orifice and annulus and drains blood from the myocardium to the right atrium. The elongate body has two states, in a first of which the elongate body has a shape that is adaptable to the shape of the coronary sinus, and to the second of which the elongate body is transferable from said first state assuming a reduced radius of curvature. Consequently, the radius of curvature of the coronary sinus is reduced. Due to the coronary sinus encircling the mitral annulus, the radius of the coronary sinus curvature as well as the circumference of the mitral annulus are reduced by the reduction of the radius of the coronary sinus. Thus, the described method takes advantage of the position of the coronary sinus being close to the mitral annulus, which makes repair possible by the use of current catheter-guided techniques. However, the described method is only useful in diseased valves where the reason for a valvular leak is caused by a dilation of the valve annulus.
For prolapsing leaflets, catheter-based methods have been presented where the two leaflets of the mitral valve are attached to each other by means of a thread (Percutaneous Edge-to-Edge provided by Edwards Lifesciences Corporation of Irvine, USA) or a clip (Evalve System provided by Evalve, Inc. of USA) creating a double opening with a shape like a bow-tie in the valve.
In cases where these methods are not useful, the valve may need to be replaced. Percutaneous replacement of heart valves are being developed for the aortic and pulmonary valves by Percutaneous Valve Technologies, Inc., now owned by Edwards Lifesciences Corporation and by CoreValve S.A. of Paris, France. NuMED, Inc. of New York, USA deliver a valve designed by Dr. Bonhoeffer for sole use in the pulmonary valve position. In all these devices, copies of normal human valves with three cusps are sewn from Glutaraldehyde-treated calf or horse pericardium tissue or bovine jugular vein tissue and mounted inside a stent. The stents from Edwards Lifesciences and NuMED are made of stainless steel and need to be dilated by a balloon, whereas the valve from CoreValve is mounted inside a self expanding stent of Nitinol. These devices from Edwards Lifesciences, NuMED and CoreValve will hereinafter be denoted stented valves. The stented valve is placed in the position of the valve it is supposed to replace and dilated, thereby pushing the leaflets and any calcified tissue away and thereby completely eliminating the remaining function of the valve leaflets. However, the stented valves are only useful in circular orifices such as the pulmonary and the aortic valves.
For the mitral valve and the tricuspid valve, no artificial valve has so far been presented for percutaneous placement. The main reason for not having access to percutaneously implantable valves in the tricuspid and in the mitral valve position is that the valve annulus is oval and the valve opening has a slit-like shape in case of a diseased mitral valve and triangular shape in case of a diseased tricuspid valve. The known stented valves are fixed to the valve annulus by means of friction caused by pressure from the stents towards the surrounding tissue in the valve opening. If the known stented valves with round circumference are introduced into the oval mitral annulus with a leaking area of slit-like shape, there will be wide open areas causing a severe leak, so called paravalvular leak, between the implanted device and the annulus. In addition, the tissue is too weak to allow a good fixation in the tricuspid and mitral orifices. Further, if a known stented valve is introduced in the mitral valve orifice, it would also create a block in the outflow of the aortic valve.
The known stented valves also have limitations in use for the pulmonary valve. The known stented valves are not suited to be implanted in children or growing juveniles, since they do not permit growths of the valve annulus. However, the most severe drawback with the known stented valves is the size of the device when mounted in delivery systems before implant. Mounting the valve inside a stent creates a huge diameter of the device catheter. The present devices are 7 to 9 mm in diameter, which is a huge diameter considering that the catheter is to be introduced through puncture holes in vessels through the skin and guided through sometimes severely calcified vessels, most of them having the same size as the device, to the target area. The diameter of such devices is half and half caused by the stent and the valve, which each is 3-4 mm thick.